It is known to establish a harrier in a well by a section of casing being removed mechanically by section milling, after which the cross section of the well is filled with cement. Such an operation is very time-consuming and thus involves large costs for an operator. The operation generally requires surface installations for separating metal chips from the drilling mud and, often, several different types of cleaning fluids are required for metal chips to be transported up from the depth of the well.
It is also known that a well plug may be established by means of a method and devices as proposed in the Norwegian patent application 20111641 entitled “Method for combined cleaning and plugging in a well, washing tool for directional washing in a well, and use of the washing tool” and in the Norwegian patent application 20120099 entitled “Apparatus and method for positioning of a fluidized plugging material in an oil well or gas well”, both filed by the present applicant.
In a well in which the portion to be plugged is provided with two or more pipe bodies placed substantially concentrically, it has turned out that the applicant's apparatus for cleaning before plugging, as described in the Norwegian patent document 20111641 mentioned, for a well provided with one pipe body, is not suitable for cleaning in a satisfactory manner. When two pipe bodies are cast together into the well, it has turned out to be difficult to remove residues of the casting material, which may be cement for example, in a satisfactory manner. This casting material may be superannuated and in such condition that it no longer meets the requirements of a barrier element in the well. Further, it has proved difficult to clean in a satisfactory way even when there is no casting material between the pipe bodies, as, when washing as described in said patent application, there will be a pressure drop in the annuli between the pipe bodies.